<template>
  <div class="root">
    <transition-group tag="div"
                      class="container">
      <div class="item"
           :class="'item'+i"
           v-for="(item,i) in items"
           :key="item.key"
           :style="{'background-color':item.color,'border':'1px solid'}"
           draggable="true"
           @dragstart="handleDragStart($event, item)"
           @dragover.prevent="handleDragOver($event, item)"
           @dragenter="handleDragEnter($event, item)"
           @dragend="handleDragEnd($event, item)">
        <div>{{item}}</div>
      </div>
    </transition-group>
  </div>

</template>

<script>

// export default {
//   name: 'App',
//   components: {
    
//   }
// }
export default {
  name: 'App',
  data () {
    return {
      items: [
        { key: 1, color: '#3883a0' },
        { key: 2, color: '#4883a0' },
        { key: 3, color: '#5883a0' },
        { key: 4, color: '#6883a0' },
        { key: 5, color: '#7883a0' },
        { key: 6, color: '#8883a0' },
        { key: 7, color: '#9883a0' }
      ],
      ending: null,
      dragging: null
    }
  },
  methods: {
    handleDragStart (e, item) {
      this.dragging = item
    },
    handleDragEnd (e, item) {
      if (this.ending.key === this.dragging.key) {
        return
      }
      let newItems = [...this.items]
      const src = newItems.indexOf(this.dragging)
      const dst = newItems.indexOf(this.ending)
      newItems.splice(src, 1, ...newItems.splice(dst, 1, newItems[src]))
      console.log(newItems)

      this.items = newItems
      this.$nextTick(() => {
        this.dragging = null
        this.ending = null
      })
    },
    handleDragOver (e) {
      // 首先把div变成可以放置的元素，即重写dragenter/dragover
      e.dataTransfer.dropEffect = 'move'// e.dataTransfer.dropEffect="move";//在dragenter中针对放置目标来设置!
    },
    handleDragEnter (e, item) {
      e.dataTransfer.effectAllowed = 'move'// 为需要移动的元素设置dragstart事件
      this.ending = item
    }
  }
}
</script>

<style>
  @import "assets/css/base.css";
  .container {
    display: flex;
    flex-wrap: wrap;
  }
  .item {
    width: 200px;
    height: 200px;
    margin: 10px;
    color: #fff;
    transition: all linear 0.3s;
  }
  .item0 {
    width: 400px;
  }

</style>
